Researchers at the University of Calgary measured the blood vessel function of 20 college students on a day when they had no breakfast and once after they ate two fast food breakfast sandwiches totaling 900 calories and 50 grams of fat. What they discovered was shocking: Just two hours after eating the sandwiches, the efficiency of the students' blood vessels had dropped by 15-20 percent, meaning that their vessels failed to fully dilate and were impeding the flow of blood.

So what caused this impact on the hearts of the subjects? Not surprisingly, researchers say it was the high levels of salt, fat and cholesterol in the meals.

While no one is likely to keel over instantly after eating a fast food breakfast sandwich, fat in arteries can build up over time and significantly increase the risk of heart attack, heart disease and stroke.

"Even one episode of eating something unhealthy can have an effect," said study co-author Dr. Todd Anderson, "and cumulatively, that can have an effect. Think before you eat."